Method for preparing a finely divided soya bean product

ABSTRACT

The invention concerns a process for the preparation of a finely divided soya product, wherein: 
     a) soya beans are dehulled dry, 
     b) the said beans are milled continuously for a short period in the presence of hot water, 
     c) this milled material is heat treated at a temperature above 148° C., the minimum residence time at 148° C. being 30 sec and the minimum residence time at higher temperatures being shorter and 
     d) this suspension is immediately passed through a back-pressure valve.

TECHNICAL FIELD

The present invention provides a process for the preparation of a finelydivided hydrated soya product incorporating all the components ofdehulled soya beans, intended to be used as a nutritional ingredient infood products such as nutritional milk substitute beverages or as afunctional ingredient, for example in ice cream.

BACKGROUND ART

U.S. Pat. No. 4,409,256 describes a process for obtaining a soya milk inwhich whole non-dehulled beans are subjected to dry milling, water isadded to form a slurry, this slurry is heat treated with steam toinactivate the anti-trypsin factors, and cooling is carried out with(flash) evaporation of water if the process is put into operationdiscontinuously, or by means of a heat exchanger if it is put intooperation continuously. The suspension is then centrifuged to separatethe hulls and the product obtained is dried.

U.S. Pat. No. 4,194,018 describes a process for obtaining an aqueoussoya suspension in which dehulled soya beans are subjected to an initialcoarse milling in the presence of water, to heat treatment with steam toinactivate the anti-trypsin factors, to cooling with (flash) evaporationand to a second fine milling. A finely divided aqueous soya suspensionis then obtained without the necessity for separating a residueincorporating insolubles.

Compared with existing processes for preparing soya milk in which thereis always a stage where insolubles are separated, the two aforementionedprocesses enable all the soya bean to be used, without thenon-solubilized residue being rejected, which enables an appreciablenutritional and economic gain to be achieved. However, in the processaccording to U.S. Pat. No. 4,409,256, the fact of operating withnon-dehulled whole beans makes it essential to remove the hulls afterheat treatment, which leads to a substantial loss of other componentsduring this operation. Moreover, the process according to U.S. Pat. No.4,194,018 calls for a second milling with a ball mill after heattreatment, which is very onerous.

As has been seen, obtaining these finely divided soya products of thesoya milk type presents a problem that has not yet been resolved by theprior art. It is desirable to be able to use all the soya bean, with theexception of the hull, whilst however attempting to minimize losses ofvaluable nutritional fractions and reduce production costs, at the sametime preserving a perfectly smooth texture and an agreeable non-oxidizedtaste.

SUMMARY OF THE INVENTION

The object of the present invention is to solve this problem anddescribes a process for the continuous preparation of a finely dividedhydrated soya product incorporating all the components of the dehulledsoya bean, wherein:

a) soya beans are dehulled dry,

b) the said beans are milled continuously for a short period in thepresence of hot water,

c) this milled material is heat treated at a temperature above 148° C.,the minimum residence time at 148° C. being 30 sec and the minimumresidence time at higher temperatures being shorter and d) thissuspension is immediately passed through a back-pressure valve.

It is of course understood that according to the invention, heattreatment is carried out at a temperature and for a period that do nothave adverse consequences for the organoleptic properties. At 148° C.,it is preferable to operate between 30 sec and 3 min.

As regards the upper temperature limit, this is not critical and is onlylimited by the organoleptic consequences.

It is preferable to operate at a temperature of up to 170° C., in whichcase the minimum treatment time is about 5 sec.

DETAILED DESCRIPTION OF THE INVENTION

The dry dehulling operation is important and should be carried out withthe minimum damage to the two cotyledons, since it is essential forobtaining a smooth suspension that is not rasping to the tongue.

In a second stage, the raw material, comprising dehulled soya beans, ismilled in the presence of water. This milling is carried out at atemperature of 60°-100° C., with a soya:water ratio of 1:3 to 1:10, andat a pH of 2.5 to 8.5. Milling is preferably carried out at atemperature greater than 80° C., for example between 85° and 95° C. fora period of the order of 10 sec, preferably 3 to 4 sec. The soya:waterratio is kept within its lower bracket so that a solution is obtainedthat can be pumped, and within its upper bracket since the solutionwould be too liquid and would give too low a protein content. The millsused are toothed mills and colloid mills and enable a suspension to beobtained in which 50% of the particles are less than 200 μm and 90% donot pass 700 μm. This first coarse milling can possibly be followed by asecond finer reduction bringing 90% of the particles down to a size lessthan 500 μm. A colloid mill is also used in this case. This operationinactivates the lipoxygenases of the bean through heat from the water,which prevents the development of any characteristic taste resultingfrom the action of these lipoxygenases on the unsaturated fatty acidscontained in the fatty substances in the soya bean.

In a third stage, the suspension is subjected to heat treatment. Heatingcan be direct or indirect and raises the temperature of the suspensionto 150°to 155° C. for a period of about 20-30 seconds. Heating ispreferably direct and the temperature of the suspension is raised to150° C. This stage completely hydrates the suspension and softens theparticles. The viscosity of the suspension increases during this stage,which assists the milling which is carried out in the following stage.This stage can for example be carried out in an ultra high temperature(UHT) device conventionally used for milk into which steam is injectedat a sufficiently high pressure to enable injection to take place intothe suspension, followed by a constant temperature tube. The UHT stagealso leads to inactivation of the anti-trypsin factors of the soya.

In a fourth stage, the suspension is immediately passed through aback-pressure valve into a chamber having a reduced pressure relative tothe pressure of the suspension on entry. The suspension is subjected toinstantaneous (flash) evaporation of steam, which increases the volumeof the suspension. On account of the instantaneous evaporation of waterabsorbed in the steam injection stage, the soya particles undergodisintegration. The fact of increasing the volume of the suspension bypassage through the back-pressure valve, suddenly increases friction andso leads to the suspension being milled in the back-pressure valve.Superheated particles can also be disintegrated at the outlet from theback-pressure valve by an explosion caused by rapid expansion of steam.The combination of heating and flash evaporation thus acts as a millingstage. A very fine hydrated suspension is thus obtained in which 50% ofthe particles have a size less than 60 μm, and 90% less than 90 μm. Thisdisintegration of the particles of the completely hydrated suspension,as well as softening of these particles, enables the said suspension tobecome smooth (absence of a sandy character in the mouth).

On account of the expansion of steam during passage through theback-pressure valve, the suspension cools to 50 ° to 120° C., accordingto the flash evaporation temperature. The suspension can also be cooledto a temperature of between 4 and 60° C.

As the suspension which has undergone heat treatment by steam injectionis sterile, it can, after cooling under sterile conditions, be filledaseptically at a temperature of between 4 ° and 60° C. as it is, that ison its own or in a mixture with for example sterilized cow's milk,without it being necessary to carry out any supplementary operation.

This suspension can be used either in yoghurts, in ice creams or inbeverages, in particular those based on milk, the said suspension beingadded in the desired quantity. For example, for ice creams, an additionis made in order to replace about 25% of skimmed cow's milk. Thisaddition is made for two reasons: either to supply a soya proteincontent, or for stabilizing the suspension obtained according to theprocess of the invention. The suspension obtained according to theprocess of the invention includes the non-solubilized but hydrated andsoftened residue. If it is desired to obtain powdered soya milk, thepresence of the residue has harmful consequences, by reason of the factthat the constituents of the said residue bind water very strongly. Thiswater is conventionally removed in tubular evaporators, and the dryingitself is then carried out in a drying tower by spraying. Now theconstituents of the residue retain water so strongly that the dry solidscontent at the outlet from the evaporator can barely exceed 18%, whichinvolves prohibitive drying costs to obtain a powder of this product.

It has been determined that the problem can be resolved if enzymehydrolysis is carried out on the suspension obtained according to theprocess described above.

The carbohydrates of the suspension are mainly polysaccharides, of thecellulose, hemicellulose, lignin and pectin types. Enzymes are thus usedwhich degrade these polysaccharides, of the cellulase, hemicellulase,pectinase, amylase, endo-glucanase, pectin-lyase,endo-polygalacturonase, pectin-esterase, endo-arabinase, β-1,4-galactanase, endoxylanase and arabinofuranosidase type. Moreover,experience shows that proteins also play a part in the phenomena ofwater retention and high viscosity. A mixture may thus be usedcomprising enzymes degrading polysaccharides as well as proteases.Enzymes may be made to act in a single stage or successively. Thehydrolysis conditions (temperature, pH, hydrolysis time and enzymeconcentration) are selected as a function of the enzymes used and of thedesired characteristics of the product (more stringent hydrolysis willgive a less viscous product). Enzyme hydrolysis is stopped by heatinactivation of the enzymes, by subjecting the suspension to atemperature of 90°-150° C. for 5 sec. to 2 min. It has finally beendetermined that water may be removed even more easily from the soyasuspension by adding an emulsifier either before the milling stage orbefore or after enzyme hydrolysis. This addition is made at aconcentration of between 0.5 and 4% of the said emulsifier with respectto dry matter. This emulsifier is selected from purified monoglycerides,preferably anionic monoglycerides.

The product can be packaged in liquid form either as a fresh product, orin aseptic packaging. It may then be used either alone, or in a mixturewith sugar and milk, or in the form of a nutritional beverage containingvitamins, mineral salts and other materials.

The product obtained can also be dried in a conventional devicecombining an evaporator and spray drying tower. Due to hydrolysis of theconstituents responsible for water retention, evaporation may be carriedout until dry solids contents of 18-40% are reached, which enables spraydrying to be carried out under economically favourable conditions. Itmay be packaged either alone, or in a mixture with sugar and milk, or tomake a nutritional drink.

The product obtained contains all the components of dehulled soya beans.It thus enables dietetic beverages to be prepared (soya milk type) witha high content of hydrolysed fibres, whilst retaining excellent physicaland organoleptic properties : ideal viscosity, easy solution of thepowder in cold or hot liquids and the absence of a sandy texture in themouth. A beverage is obtained which has a smooth character in the mouthand is stable on storage. This powder can also be used as an additive toyoghurts and ice creams.

According to the invention, soya pulp obtained from the manufacture ofsoya milk may also be treated. In this case, this pulp is heat treatedat a temperature greater than 148° C., the minimum residence time at148° C. being 30 sec, the minimum dwell time at higher temperaturesbeing shorter, and this pulp is immediately passed through aback-pressure valve. Heat treatment and the flash evaporation stage isthus the same as for soya bean. What has been said previously for heattreatment also remains valid for soya pulp.

The invention is illustrated in greater detail in the followingpractical examples.

EXAMPLE 1

Dehulled soya beans were milled in the presence of water previouslyraised to a temperature of 90° C., in a soya:water ratio of 1:5.7 for 5sec. This suspension was then passed through a direct steam injectiondevice, where it was instantaneously raised to 150° C. It then passedalong a constant temperature tube under a pressure of 5.7 bars for 30sec. The suspension then passed immediately through a back-pressurevalve and entered a chamber under reduced pressure (0.16 bar). Thistreatment led to a reduction in the size of the particles and to asmooth structure for the suspension. It was cooled instantaneously to55° C., by flash-evaporation. Samples taken from the outlet of the milland from the outlet of the vacuum chamber exhibited the followingproperties:

    ______________________________________                                                                   Outlet from vacuum                                 Sample        Outlet from mill                                                                           chamber                                            ______________________________________                                        50% of particles                                                                            140 μm    37.5 μm                                         with a diameter less                                                          than                                                                          90% of particles                                                                            650 μm      85 μm                                         with a diameter less                                                          than                                                                          ______________________________________                                    

EXAMPLE 2

The conditions of example 1 were repeated, with the exception of themilling stage, which was carried out twice: an initial coarse millingfollowed by colloid milling. The following table gives the properties ofthe suspension obtained.

    ______________________________________                                                  Outlet 1  Outlet 2 from                                                                             Outlet from                                   Sample    from mill mill        vacuum chamber                                ______________________________________                                        50% of    165 μm 165 μm   40 μm                                      particles with                                                                a diameter                                                                    less than                                                                     90% of    600 μm 460 μm   85 μm                                      particles with                                                                a diameter                                                                    less than                                                                     ______________________________________                                    

The same conditions were then used as in example 1. The productsobtained did not exhibit any differences compared with those in thatexample.

EXAMPLE 3

The same conditions as in example 1 were repeated, with the exception ofthe heat treatment which was carried out at 170 ° C. for 5 sec.

The following table gives the properties of the suspension obtained.

    ______________________________________                                                                   Outlet from vacuum                                 Sample        Outlet from mill                                                                           chamber                                            ______________________________________                                        50% of particles                                                                            176 μm    42 μm                                           with a diameter less                                                          than                                                                          90% of particles                                                                            641 μm    83 μm                                           with a diameter less                                                          than                                                                          ______________________________________                                    

EXAMPLE 4

Part of the suspension from example 1 was taken as a control sample. Theremainder of the suspension was divided into 3 portions A, B and C. Twoenzyme mixtures were also prepared:

mixture PROT containing a mixture of proteases

mixture POLYS containing a mixture of enzymes degrading polysaccharides.The following table summarizes the enzyme treatments of the differentsuspension samples.

    ______________________________________                                                                           Temperature                                Portion  Enzymes   pH      Time (min)                                                                            (°C.)                               ______________________________________                                        A        PROT      6.7     20      55° C.                              B        PROT +    6.8     20      55° C.                                       POLYS                                                                C        Two stages:                                                                   1) POLYS  6.7     20      55° C.                                       2) PROT   6.7     20      55° C.                              Control                                                                       ______________________________________                                    

The quantities of enzymes used were 0.1% for POLYS and 0.05% for PROT (%pure enzyme with respect to the dry matter in the suspension).

Inactivation of the enzymes in each portion was carried out by a 10 secheat treatment at 110° C.

The following table summarizes the viscosities of the different samplesin this stage.

    ______________________________________                                               Portion                                                                             Viscosity                                                        ______________________________________                                               A     High                                                                    B     Low                                                                     C     Low                                                                     Control                                                                             High                                                             ______________________________________                                    

The dry solids content of the different portions was 14% afterhydrolysis. Each portion was then transferred to an evaporator. Thefollowing table shows the dry solids content obtained at the outlet fromthe evaporator: Portion Dry solids content at the outlet from theevaporator

    ______________________________________                                                   Dry solids content at the                                          Portion    outlet from the evaporator                                         ______________________________________                                        A          18%                                                                B          26%                                                                C          26%                                                                Control    18%                                                                ______________________________________                                    

Drying was then carried out by spraying the different samples, and thepowder obtained was reconstituted in water. The following tablesummarizes the properties of the beverage obtained:

    ______________________________________                                        Portion     Properties of the reconstituted beverage                          ______________________________________                                        B and C     excellent texture in the mouth                                                excellent dissolving properties                                   Control     thick sandy texture                                                           poor dissolving properties: white spots on                                    the glass wall                                                    ______________________________________                                    

EXAMPLE 5

Soya pulp as obtained in the production of soya milk was taken again.This pulp was rediluted to a dry solids content of 6%. This suspensionwas then passed through a direct steam injection device, where it wasraised to 150 ° C. It then passed through the constant temperature tubeunder a pressure of 5.7 bar for 30 sec. The suspension then immediatelypassed through a back-pressure valve and entered the chamber underreduced pressure (0.16 bar). This treatment led to a reduction in thesize of the particles and a smooth structure for the suspension. Thesuspension cooled to 55° C. by flash evaporation. A product was obtainedhaving the following properties:

    ______________________________________                                                      Pulp after re-                                                                              Exit from the                                     Sample        dilution in water                                                                           vacuum chamber                                    ______________________________________                                        50% of particles                                                                            153 μm     40 μm                                          with a diameter less                                                          than                                                                          90% of particles                                                                            585 μm     88 μm                                          with a diameter less                                                          than                                                                          ______________________________________                                    

EXAMPLE 6

This example describes the preparation of an ice cream where the milkpart was partially replaced by soya. A suspension was prepared asdescribed in example 1.This suspension was then used directly andincorporated in the liquid mixture of the ice cream in the followingproportions:

    ______________________________________                                                     Recipe without soya                                                                          Recipe with soya                                               (%) dry solids (%) dry solids                                    Ingredient   content        content                                           ______________________________________                                        Skimmed milk powder                                                                        10              7                                                Soya suspension                                                                            ./.             3                                                Other ingredients                                                                          25             25                                                (fats, powdered milk                                                          whey, sugars,                                                                 emulsifiers and                                                               stabilizers)                                                                  Water        65             65                                                             100            100                                               ______________________________________                                    

This mixture was then deep frozen and an ice cream based on milk andsoya was obtained.

Compared with the recipe without soya, ice cream thus prepared showed aricher structure and improved storage stability.

EXAMPLE 7

This example describes the preparation of ice cream where the milk partwas partially replaced by soya pulp.

A suspension was prepared as described in example 5.This suspension wasthen used directly and incorporated into the liquid mixture of the icecream in the following proportions:

    ______________________________________                                                     Recipe without soya                                                                          Recipe with soya                                               (%) dry solids (%) dry solids                                    Ingredient   content        content                                           ______________________________________                                        Skimmed milk powder                                                                        10              9                                                Soya suspension                                                                            ./.             1                                                Other ingredients                                                                          25             25                                                (fats, powdered milk                                                          whey, sugars,                                                                 emulsifiers and                                                               stabilizers)                                                                  Water        65             65                                                             100            100                                               ______________________________________                                    

This mixture was then deep frozen and an ice cream based on milk andsoya was obtained.

Compared with the recipe without soya, ice cream thus prepared showed aricher structure and improved storage stability.

EXAMPLE 8

This example describes the preparation of a nutritional beverage basedon whole dehulled soya beans and its aseptic filling.

Dehulled soya beans were milled in the presence of a solution containingall the other ingredients previously raised to a temperature of 90° C.,in a soya:water ratio of 1:5.7 for 5 sec. This suspension was thenpassed through a direct steam injection device, where it was raised to150° C. It then passed through the constant temperature tube at apressure of 5.7 bar for 30 sec. The suspension then immediately passedthrough a back-pressure valve and entered the chamber under reducedpressure (0.16 bar). This treatment led to a reduction in the size ofthe particles and a smooth structure for the suspension. The suspensionwas cooled to 55° C. by flash evaporation.

    ______________________________________                                                         Recipe                                                       Ingredient       % dry solids content                                         ______________________________________                                        Soya              5                                                           Other ingredients (fats,                                                                       10                                                           sugars, flavours, emulsifiers                                                 and stabilizers)                                                              water            85                                                                            100                                                          ______________________________________                                    

As this beverage was sterile since it had been subjected to heattreatment by steam injection, it was filled aseptically, after coolingunder sterile conditions.

EXAMPLE 9

This example describes the preparation of a powdered nutritionalbeverage based on cow's and soya milk.

A suspension was prepared as in example 1.This suspension was then mixedwith all the other ingredients and then dried by atomization. A powderednutritional beverage was obtained.

    ______________________________________                                                   Composition of the                                                                            Composition of the                                            powder without soya                                                                           powder with soya                                              (%) dry solids  (%) dry solids                                     Ingredient content         content                                            ______________________________________                                        Cow's milk 60.6            33.8                                               Soya       ./.             23.0                                               Other ingredients                                                                        36.4            40.2                                               (sugars flavours,                                                             emulsifiers and                                                               stabilizers)                                                                  Water      3               3                                                             100             100                                                ______________________________________                                    

We claim:
 1. Process for the preparation of a finely divided soyaproduct, which comprises the steps of:(a) dehulling dry soya beans; (b)continuously milling the beans in the presence of hot water to produce amilled material of a plurality of particles; (c) heat treating themilled material for a residence time of at least 5 seconds to 3 minutesat a temperature of from 148° C. to 170° C. to produce a suspension,wherein the residence time decreases as the temperature increases, withthe residence time at 148° C. being at least 30 seconds and theresidence time at higher temperatures being shorter; (d) directlypassing the suspension to a flash evaporation step; and (e) flashevaporating water from the suspension to reduce the size of theparticles due to explosive pressure from the evaporating water. 2.Process according to claim 1, characterized in that milling takes placewith water at a temperature greater than 80° C. and lasts for about 10sec, preferably about 3-4 sec.
 3. Process according to claim 1, whereinthe heat treating step is carried out by steam injection at atemperature of between 150° and 155° C. for about 20-30 seconds. 4.Process according to claim 1, wherein the milling step comprises acoarse milling stage and a fine milling stage.
 5. Process according toclaim 1, wherein the milling step is carried out with a soya:water ratioof 1:3 to 1:10, and at a pH of 2.5-8.5.
 6. Process according to claim 1,wherein the suspension is cooled to a temperature of less than 60° C.during the flash evaporation step.
 7. Process according to claim 6,characterized in that aseptic filling of the suspension is carried out,either alone, or in a mixture at a temperature of between 4° and 60° C.8. Process according to claim 1, wherein enzyme hydrolysis is carriedout on the suspension following flash evaporation.
 9. Process accordingto claim 8, wherein enzyme hydrolysis is carried out in at least onestage by an enzyme degrading polysaccharides or a mixture of enzymesselected from the group consisting of proteolytic enzymes and of enzymesdegrading polysaccharides.
 10. Process according to claim 8, wherein amixture of enzymes is used comprising at least one enzyme degradingpolysaccharides and at least one proteolytic enzyme.
 11. Processaccording to claim 10, wherein at least one enzyme degradingpolysaccharides is selected from the group consisting of celluloses,hemicelluloses and pectins.
 12. Process according to claim 8, whereinthe enzyme hydrolysis stage is followed by drying of the hydrolysedsuspension.
 13. Process according to claim 1, wherein the flashevaporating step is conducted to provide 50% of the particles with asize of less than 60 μm and 90% of the particles with a size of lessthan 90 μm.
 14. Process according to claim 1, further comprising addingwater to the flash evaporated particles to reconstitute the particlesinto a soya powder suspension. wherein 50% of the soya powder particleshave a size less than 60 μm and 90% of the soya powder particles have asize less than 90 μm.
 15. Process of preparing a product which comprisespreparing the aqueous suspension according to claim 14, and adding thissuspension in an amount of up to about 25% by weight of the product to ayogurt ice cream or a beverage to prepare the product.
 16. Process forthe preparation of a finely divided soya product from a solution of soyapulp particles and water, which process comprises the steps of:heattreating the solution of soya pulp particles at a temperature of 148° C.to 170° C. for a residence time of at least 5 seconds to 3 minuteswherein the residence time decreases as the temperature increases, withthe residence time at 148° C. being at least 30 seconds and theresidence time at higher temperatures being shorter; directly passingthe heat treated soya pulp particles to a flash evaporation step; andflash evaporating water from the pulp to reduce the size of theparticles due to explosive pressure from the evaporating water. 17.Process according to claim 16, wherein the pulp is heat treated at atemperature of greater than 148° C. to about 170° C. for a time ofbetween about 5 seconds and 3 minutes with shorter times utilized athigher temperatures in the range.
 18. Process according to claim 16,wherein the heat treatment of the solution is carried out by steaminjection at a temperature of between 150° C. and 155° C. for about 20to 30 seconds, and the flash evaporating step is conducted to provide50% of the particles with a size of less than 60 μm and 90% of theparticles with a size of less than 90 μm, enzyme hydrolysis is carriedout on the solution following flash evaporation, the pulp particles arecooled to a temperature of less than 60° C. during the flash evaporationstep, and water is then added to the cooled particles to form asuspension.